1. Field of the Invention
This invention relates to air gun subarrays used in marine seismic surveying, and more specifically to an apparatus for distributing a lubricant to air guns in a single airline air gun subarray.
2. Discussion of the Prior Art
In marine seismic surveying, air gun arrays or subarrays are frequently used as acoustic transmitters. Several subarrays are pulled simultaneously by a vessel at a predetermined depth below the water surface in a body of water, usually the sea. One type of subarray contains several spaced-apart air gun stations connected in series, each station containing at least one air gun. To operate the air guns, air at high pressure, which can easily exceed 1500 psi, is supplied to all air guns from a single airline. To increase the working life of each air gun and to reduce regular maintenance, it is necessary to supply adequate amount of a lubricant to each air gun in the subarray during operation. One method which has been utilized to supply a lubricant to the air guns is to supply an air-lubricant mixture to the single airline. A problem exists with respect to the proper distribution of the lubricant to the air guns. The lubricant, being the heavier component of the air-lubricant mixture, drops out and is utilized at the first several air gun stations, leaving very little or no lubricant for the back air gun stations. This can significantly reduce the working life of the air guns and also require frequent servicing and maintenance of the air guns in the back stations which are cost prohibitive for each air gun costs several thousand dollars to manufacture and the maintenance is labor intensive.
The present invention provides an apparatus for use with an air gun in the single airline subarray to supply only a certain amount of lubricant to that gun, thereby permitting the remaining lubricant in the air-lubricant mixture to go to the subsequent guns.